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Re: Ok guys, get ready to rip !!

Originally posted by bornriding Nathan,

I'm going to get blasted for this...but here goes !
Having any system that uses a variable speed motor without a subseguent reducal in BTU output. In other words, a two speed system may have a two speed blower & a two speed compressor for two different levels of cooling. And this is very efficient.
But, if you just have a variable speed blower without a two or more speed compressor, then you only save the difference in energy between the variable speed motor & the single or two speed motor.
By my calculations, you would save less than $10.00 / year for that differance in blowers, and yet that variable speed blower will cost you several hundred dollars more to install it and many hundreds more to replace it. To me that is 'no payback'.
And the only benefit that you would receive, is a little lower humidity level. So, do you have a problem with humidity ?? It may be worth the var. sp. Just realize that you are spending hundreds for a small comfort difference.

OK guys, I can take it !!! LOL

I was under the impression that the VS airhandlers had ECM motors which could be programmed to deliver a set amount of CFMs regardless (to a point) of the ESP. In other words, an ECM motor can compensate for duct issues (to a point). Isnt this the real reason to get a VS airhandler? Thoughts?

So it appears that most professional members would opt for the variable speed fans. The Trane website seems to show that variable speed is reserved for the higher efficiency units, although Trane does show an 80% furnace with variable speed. I had decided to go for a 12 or 13 SEER AC unit and a 2-stage 80% furnace.

So is it the case that usually manufacturers will not put a variable speed fan on a 12 or 13 SEER AC unit? Can you recommend another manufacturer that would offer the VS on a lower efficiency unit?

Nathan
Currently GE is the only manufactuer of ecm motors so no matter who you buy Carrier, Trane York it is virtually the same motor, the only difference in my understanding is the controller might be set up different by manufacturers. It is still a better option than a two speed psc motor. These ecm motors are a three phase dc motor in other words they are built really tough. I do not know about anybody else but I have never seen a motor failure yet, but have seen some of the controllers go out. Have seen more than my share of psc motors failures. Take the advice of many of the pros and buy a VS motor. As for the argument about savings, I am not sure that I believe what he said about it only being a marginal amount. I see the cost cut in about 1/10, Trane has some numbers some where. I can dig them out if you are interested.

Not to be repetitive, but it still seems as though I have to buy a unit, whatever the brand, that comes with a VS, or ECM, already installed. Apparently you can't, or shouldn't install an ECM on a unit that was not designed for it.

For example, the Trane XL13i AC unit has a 2 speed fan, and the Trane XL 80% has a 4 speed fan. While Trane does offer an XL 80% furnace with a variable speed fan, apparently you have to buy a 15 SEER AC unit to get a variable speed fan.

I would like the VS fan but I would prefer not to have to spend the money on a higher SEER unit.

No slam on my contractor. I haven't spoken to him yet about this. I was just getting the information from the Trane website. It's apparent I can get a VS 80% furnace, although it may be a little more difficult to find a VS lower SEER AC unit.

beenthere, I'm not looking for a 2 stage AC, just a single stage with a variable speed fan. Perhaps there are units offered that combine a 12 or 13 SEER with VS fan, but the manufacturer websites I checked (Carrier, Trane, York) don't have that combination. Again, there may be models not reflected on the websites.

Beenthere

Just a question.
Once any system has reduced the humidity to an acceptable level, then how much more de-humidifing does it need to do??
In other words, the first time you turn on your system, it will cool the home down to its set temperature, and with variable speed, lower the humidity, lets say 5 pts.So we went from 50% relative hum. with my 1-speed to 45% rel. hum with var.sp. Then 1 hour or two later, the unit comes back on. The temp has risen about 2-3 degrees. How much humidity has been added then. Does the humidity level return to 50% or higher ?? Otherwise, when the unit again reaches its set temp, with var sp., I may have lowered the hum to 40 -42 %
and so forth. When is my humidity level low enough??
And when the VS blower comes on and off thereafter doesn't it produce less & less humidity control.

No, I'm nuts. I'm a CPA trying to do audits and taxes here in California finding that I find this forum to be a really entertaining diversion to the work I need to get out. As to your point, I wish I had the technical expertise to offer an intelligent response. Docholiday did tell me in a previous post that comfort with a 2 stage VS furnace would be more important than a VS AC unit in my low humidity area. If I cannot locate a lower SEER VS unit (single stage) it won't be a big deal. I'll just get an 80% 2 stage VS furnace and a single stage single speed AC unit (12 or 13 SEER).